1. Field of the Invention
The present invention relates generally to a semiconductor process and three MOS transistor processes, and more specifically, to a semiconductor process having a dielectric layer including metal oxide and three MOS transistor processes including a gate dielectric layer having a high-k dielectric constant.
2. Description of the Prior Art
Poly-silicon is conventionally used as a gate electrode in semiconductor devices, such as the metal-oxide-semiconductor (MOS). However, with a trend toward scaling down the size of semiconductor devices, the conventional poly-silicon gate has faced problems such as inferior performance due to boron penetration and an unavoidable depletion effect which increases the equivalent thickness of the gate dielectric layer, reduces gate capacitance, and worsens a driving force of the devices. Therefore, work function metals have been used to replace the conventional poly-silicon gate, to be the control electrodes suitable for use as the high-K gate dielectric layer.
A gate dielectric layer having a high-k dielectric constant(High-K) directly formed on the substrate or formed on the substrate through a buffer layer often entrains some gases or bonding such as vapor, hydrogen-oxygen bonding etc., which is either not needed, or actually worsens the performance of semiconductor elements. Furthermore, a more serious problem is that oxygen-related vacancies, which trap charges, occur because of oxygen particles in the gate dielectric layer breaking away from the gate dielectric layer, giving rise to the equivalent thickness of the gate dielectric layer increasing and the threshold voltage shifting. This reduces the electrical performance of the transistors.